Reza Asadi

Combining micro- and nano-texture to fabricate an antireflective layer

We combined photonic crystal (PC) and nanoporous structures in silicon (Si) to decrease the reflectance of the Si surface. Due to gradual increase of effective refractive index in this structure, reflection is reduced drastically over a broad spectral range. A two-dimensional Si PC was fabricated by interference lithography, then a nanoporous structure was made on the PC by using metal-assisted chemical etching. The obtained reflectance is about 3% across a spectral range of 400 to 2000 nm. This indicates an improvement of reflectance up to 90% compared to bare Si.

Efficiency Enhancement of PtSi Detectors by Photonic Crystals

We present the first experimental study for enhancement of PtSi Schottky detectors using photonic crystal (PC) structures. PCs can be used for simultaneous reduction of reflection and increase of absorption. The 2-D PCs are fabricated by interference lithography and reactive ion etching. In PC with 4.2-μm depth, the average responsivity is enhanced by a factor of ~7 with respect to regular detectors. We show that the light absorption enhancement is not sufficient to explain efficiency enhancement. The extra enhancement may be due to nanoscale roughness on the PC walls that affect the carrier collection efficiency and cutoff wavelength.

Fabrication of Metal Nanocomposite Photonic Crystal for Switching

In this study, we fabricate a nanocomposite photonic crystal (PC) by doping low concentration gold nanoparticles in a one-dimensional slab polymer PC. By coating a ZnS layer, we get a fairly sharp Fano resonance dip with quality factor about 30 in the transmission spectrum of the PC near the surface plasmonic resonance of gold nanoparticles. We show theoretically that in spite of absorption by the gold nanoparticles this nanocomposite PC can be used as a good switch with low pump threshold intensity, high contrast, and high efficiency.

Fabrication of optical ridge waveguide in lithium niobate by argon sputtering and titanium self-alignment in-diffusion

Abstract. We report a simple way of etching lithium niobate (LN) to build ridge waveguides. Argon plasma is used in an RF-sputtering chamber to etch the LN. The height of waveguide walls reaches 2.5  μm and a titanium self-alignment in-diffusion process is used to make the waveguide. Several diffusion times and different waveguides width are used to compare the mode properties and proportion of light that is confined in the ridge section of the waveguide.